Structures for either removing ice accretions from surfaces or preventing the accretion of ice on suseptible surfaces such as those associated with wings, tail surfaces, and struts of aircraft are well known. Where such devices prevent the accumulation of ice the devices are called anti-icers.
Where such devices periodically remove ice accumulations, the devices are frequently referred to as de-icers.
Anti-icers typically include two basic approaches, one approach being the introduction on to the surface of a fluid having an inherent property of suppressing the formation of ice; the second being the heating of an ice accreting surface to maintain a continuous surface temperature sufficiently elevated to foreclose the formation of ice thereover. For de-icers, de-icing methods typically fall into one of three categories, one being the introduction of a fluid beneath ice accumulations upon the ice accreting surface to weaken the bond between the surface and the ice thereby allowing the force of fluid such as air moving over the surface to remove the ice; the second being the heating of the surface periodically to weaken the bond between the surface and the ice to allow removal by the airstream; the third being periodic distortion of the ice accreting surface by inflating, for example, a Pneumatic de-icer applied thereover.
With respect to thermal means for anti-icing or de-icing ice accreting surfaces, heating is typically accomplished by either the use of electrothermal pads applied over or immediately beneath an ice accreting surface or by the introduction beneath the ice accreting surface of a fluid, such as gases drawn from a compressor stage of a turbine engine, sufficiently elevated in temperature to provide a desired anti-icing or de-icing function. Where anti-icing is to be accomplished, typically any source of heat employed in effecting anti-icing is operated in a continuous manner. So, electrothermal pads employed for anti-icing are generally activated continuously during those time periods wherein anti-icing capability is desired.
Conversely, for de-icing capability, electrothermal pads are typically operated intermittently. Intermittent operation is desirable in part because of the weight and power consumption characteristics of electrical generating equipment necessary for the operation of electrothermal de-icing pads. By operating such pads for timed periods only, and sequencing the operation of such pads so that relatively few are operating during any particular time period, the size and power drain associated with electrical generating equipment sufficient to support electrothermal de-icing is significantly reduced.
In order that electrothermal de-icing pads be operated in an orderly, sequenced fashion, each for a desired time period, it has been necessary to provide timer-sequencers operably connected to the de-icer pads and a source of electrical current employed in operating the de-icer pads configured to sequence properly application of electrical current to electrothermal pads. Typically, such timer-sequencers or timer controllers have included an electro-mechanical device configured to apply sequentially, electrical current for desired time periods to various electrothermal de-icing pads aboard an aircraft. These de-icer pads represent in such application electrical loads within a load circuit that begins with a source of electrical current and ends at a point of low reference voltage by which the electrical current flow returns to the source of electrical current after passing through the loads.
In electro-mechanical timer-controllers, the current flowing to a particular load flows through the timer- controller via contacts within the mechanical sequencing device. The electro-mechanical sequencing device or timer conroller, by reason of the large current flows therethrough, must by necessity include contacts having a relatively elevated surface area and configured to transfer large electrical currents flowing to the loads through the mechanical sequencer. As a consequence, these electro-mechanical sequencers typically require powerful electrical activators configured to effect changes typically by means of rotation of contacts within the electro-mechanical sequencer, necessary to overcome frictional interference between engaging contacts within the electro-mechanical sequencer. These large electrical actuators for such electro-mechanical sequencers coupled with a fairly bulky physical configuration for such sequencers by dint of the presence of relatively large, electrically conductive current transferring contacts within the sequencer tends to make such electro-mechanical timer-controllers heavy. With weight being at a premium on most aircraft, it is desirable that weight associated with timer-controllers be reduced to the extent possible.
Equally, movement of any electro-mechanical sequencer in such timer-controllers has traditionally been dictated by a mechanical clock activating the electrical actuator typically to rotate contacts within the electro-mechanical timer sequencer to the next sequence position. Such clocks also have tended to be bulky and, fairly heavy, and accordingly, a timer-controller effective in reducing the weight and bulk required for such clock mechanisms could find substantial utility in the manufacture of timer-controllers for use in aircraft de-icing systems.
Traditionally, timer-controllers have utilized one or more ammeters to inform operating personnel of an aircraft employing a timer-controller for controlling sequential de-icing processes as to the quantity of electrical current flowing to any particular de-icer during sequenced operation. Aircraft operating personnel by necessity were required to observe the ammeter to assure that malfunctions within one or more of the de-icing pads was not causing a disruption in de-icing function. Observation of a low or a particularly elevated electrical current flow based on ammeter readings would be an indication to the aircraft operator that the de-icing function was not as desired with respect to one or more de-icing pad.
Pilots, however, in operating aircraft have a large number of activities to accomplish. Accordingly, systems that Provide a go/no-go indication with respect to various functions aboard an aircraft have gained popularity. Particulary with respect to de-icers, a go/no-go indication employing, for example, red and green lights, could find substantial utility in the manufacture of de-icing systems for aircraft.